PRIMARY SITES OF ENERGY DEPOSITION 

 ASSOCIATED WITH RADIOBIOLOGICAL 



LESIONS 



L. H. Gray 



British Empire Cancer Campaign Research Unit in Radiobiology, 

 Mount Vernon Hospital, Northwood 



The concern of this symposium is with metaboUc pathways 

 in the development of radiobiological damage. Direct ob- 

 servation of the metabolic activity of the irradiated cell may 

 hit the trail early or late. It may possibly be a help in inter- 

 preting observations of metabolic activity to consider whether 

 there is any independent evidence as to where any of the 

 pathways begin. The evidence might in principle be either 

 chemical or anatomical. 



In the study of biological damage induced by u.v. radiation, 

 useful information has been obtained by comparing "action 

 spectra" with absorption spectra. Mutation, chromosome 

 fragmentation, inhibition of colony formation, are among 

 the effects which are usually associated with the nucleotide 

 type of absorption, while spheration of the nucleolus and 

 spindle damage are among those in which the primary energy 

 absorption appears to be in protein. The study of biological 

 damage induced by u.v. radiation and radiomimetics, how- 

 ever, gives us no reliable evidence concerning damage induced 

 by ionizing radiations, since many cases are known in which 

 the damage induced by these several agents proceeds, at 

 least in part, by different pathways (Gray, 1954). 



Ionizing radiation delivers energy to atoms in a highly 

 localized, but unselective, manner, almost regardless of the 

 molecular configurations of which they form a part. The 

 types of chemical change which follow in small and large 

 molecules have been described by Dale and Butler (this 



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